1. Field of the Invention
The present invention relates to the petroleum industry, and more particularly, to the optimization of the location of wells, or drainage zones, in a petroleum reservoir in order to produce hydrocarbons.
2. Description of the Prior Art
To produce a petroleum reservoir, reservoir engineers want to define the best positions and trajectories for the wells to be drilled, corresponding to the best drainage zones. These wells are generally production wells allowing hydrocarbons to be driven from the reservoir to the surface, or sometimes injection wells, for example water or gas injection wells, intended to improve the recovery of hydrocarbons contained in the reservoir.
Well drilling is an important decision in the life of a petroleum reservoir insofar as drilling a well is both time and cost consuming. Reservoir engineers therefore generally use two tools:
A first tool is referred to as “reservoir model” that provides an image representative of the structure of the reservoir and of the behavior thereof. This image or representation is constructed from data collected in the petroleum field being considered (cores, logs, seismic data, etc.) and obtained by geologists, geophysicists, petrophysicists and uses a programmed computer. However, in practice, geologists, geophysicists and petrophysicists do not have enough data for constructing a model on the computer that would perfectly correspond to the subsoil. The usual known approach therefore constructs several reservoir models representing different properties such as petrophysical properties for example. Each reservoir model is considered to be a possible image of the structure of the reservoir and of the behavior thereof. The uncertainty on the precise knowledge of the reservoir is thus accounted for by producing several possible reservoir images.
A second tool is referred to as “flow simulator”. A flow simulator is software intended for modelling fluid flows within the petroleum reservoir represented by a reservoir model. For example, this software allows assessment, for a given well configuration and for a given time interval, the amounts of water, oil and gas produced. PumaFlow® (IFP Energies nouvelles, France) is an example of a commercially available flow simulator.
There are known techniques for optimizing the location of drainage zones using several possible reservoir models and a flow simulator.
The following methods are, for example, known:    Guyaguler, B. and Home, R. N. 2001. Uncertainty Assessment of Well Placement Optimization. In: SPE Annual Technical Conference and Exhibition. SPE 71625,    Ozdogan, U. and Home, R. N. 2006. Optimization of Well Placement Under Time-Dependent Uncertainty. SPE Res Eval & Eng 9 (2): 135-145. SPE-90091-PA,    Alhuthali, A. H., Datta-Gupta, A., Yuen, B. and Fontanilla, J. P. 2010. Optimizing Smart Well Controls Under Geologic Uncertainty. Journal of Petroleum Science and Engineering 73 (1-2): 107-121,    Schulze-Riegert, R., Bagheri, M., Krosche, M., Kuck, N. and Ma, D. 2011. Multiple-Objective Optimization Applied to Well Path Design Under Geological Uncertainty. In SPE Reservoir Simulation Symposium. SPE 141712.
However, these approaches represent a long and burdensome process requiring a very large number of flow simulations using the flow simulator. Indeed, for each drainage zone configuration being considered, these methods perform a flow simulation for each possible reservoir model, and combine them afterwards using a quality criterion, conventionally defined as a parameter referred to as “Net Present Value” or NPV. The NPV is the cash flow difference generated by the investment corresponding to the drainage zones placement.
In order to meet the needs of engineers and of specialists in charge of the petroleum reservoir development, it is essential to reduce the number of flow simulations to optimize the placement of drainage zones on several possible reservoir models.
The following document describes a method for reducing the number of flow simulations:    Wang, H., Echeverria Ciaurri, D., Durlofsky, L. J. and Cominelli, A. 2011. Optimal Well Placement Under Uncertainty Using a Retrospective Optimization Framework. In: SPE Reservoir Simulation Symposium. SPE 141950-MS.
This method uses a limited number (selected by the engineer or the user of the method) of reservoir models at the start of the optimization stage, then it uses more and more (as selected by the engineer or the user of the approach) models according to the evolution of the optimization. In practice, it is difficult for the engineer to choose the number of models to be used in each stage or iteration of the method. Furthermore, during the last generations for each drainage zone configuration a large number (21 or 104 in the example presented) of possible reservoir models are considered and thus a large number of reservoir simulations for each drainage zone configuration. In practice, it is also very difficult to carry out this large number of flow simulations.